A cursory look at the V8 source seems to show that it delegates sorting to std::sort which in libstdc++ (gcc) is Introsort (a hybrid Quicksort + Heapsort).
Yeah, for someone not used to the code it's tough. The "insider knowledge" is that builtins defined in .tq files (files compiled by the Torque compiler[0]) are added to entries in the Builtins enum, which itself is defined as a giant macro[1] that pulls in a Torque generated macro[2]. In the bootstraper (which sets up the standard library), the Builtins::kArrayPrototypeSort builtin is installed as "sort" onto Array.prototype[3], which means you should grep for "ArrayPrototypeSort", which is defined in the linked .tq file.
